Orthomyxoviridae Flashcards
(26 cards)
What are the 4 genera of orthomyxoviridae?
- influenza A: human, swine, equine, canine, birds, seal
- influenza B: human
- influenza C; human, swine
- influenza D: swine, cow
- thogotovirus: tick borne viruses
Influenza outbreaks in humans
- 1918: Spanish flu (H1N1) = 40 million deaths
- 1957: Asian flu (H2N2) = 2 million deaths
- 1968: Hong Kong flu (H3N2) = 1 million deaths
- 2009: H1N1
Possible HA-NA combinations among type A influenza viruses
HA subtypes: 1-18
NA subtypes: 1-11
= 198 HA-NA combinations
Antigenic drift
Accumulating point mutations in RNA segments coding for HA and H A
- results in minor antigenic changes in NA and HA
- new variants still possess same HA and NA subtypes
- linear progression
- horses, swine, equine
Antigenic shift
Gene reassortment when one cell is infected with 2 different flu A viruses
_____ facilitates emergence of pandemic strains
Reassortment
Emergence of highly pathogenic avian influenza viruses
Associated with mutation at the cleavage site in HA molecule
- point mutations, nucleotide inserts, recombination
- all HPAIVs have been H5 or H7, but few H5 and H7 AIVs are HP (majority are LP)
______ serves as a mixing vessel for influenza A viruses
Swine!
- have both receptors (alpha 2,3 and 2,6- linked sialic acid
Avian influenza in US poultry
LPAI viruses
- no clinical illness, drop in egg production, respiratory disease
- poultry can become a reservoir!!
HPAIV can cause severe respiratory disease as well as _______
Neurological disorders
Interspecies transmission in birds
LPAI viruses are host adapted!
- LPAIVs cross species barriers with difficulty
- viruses replicate poorly in hosts
- require adaptation to new host
Animal influenza vaccines
- equine: H3N8 and H7N7 inactivated
- swine: H1N1, H3N2 inactivated
- canine: H3N8 inactivated (no H3N2!!!)
- avian: only available for turkey in some US states
What are 3 current challenges for influenza?
- natural history of H5 HPAI
- pathogenesis (genomic constellation)
- control: education, biosecurity, depopulation, vaccination
Influenza viruses are divided into groups based on their ______
Antigenic differences in nuclear protein and matrix protein, and genetic variations
- influenza A is further classified based on antigenic difference among neuraminidase and hemagglutinin
Influenza A genome
8 segmented, single stranded, negative sensed RNA
What are the 4 major antigens of influenza?
H, N, M, and NP
- only antibodies to H and N glycoproteins are associated with resistance to infection
Antigenic drift results in ________
Imperfect protection by old vaccines
- detected by 2-4 fold increase in HI titer between one isolate and the mutant recovered several years later
Antigenic shift results in _______
No protection by old vaccines
Birds that survive influenza infection can excrete the virus ______
Orally or in feces for at least 10 days
Respiratory signs of avian influenza
Excessive lacrimation, sinusitis, diarrhea, edema of head, wattles, and comb
What is the natural reservoir of avian influenza viruses?
Migratory waterfowl, wild ducks
_____ or ______ contact of domestic flocks with wild migratory waterfowl is a frequent cause of epidemics
Direct or indirect
T/F: viruses of low pathogenicity can mutate into highly pathogenic strains
True, after circulation in a poultry population
The best specimen for diagnosis is _______
Nasal mucus taken at early stage or lung tissue obtained at necropsy
